THE INTERACTION OF DUST, TOPOGRAPHY, AND PEDOGENESIS IN VOLCANIC TERRAIN OF THE SOUTHWESTERN U.S

Pedogenesis in the semiarid volcanic terrain of the southwestern U.S. is controlled by complex interactions among parent material, topography, and external inputs. The work presented here investigates these interactions across a range of Quaternary landscapes in Arizona and New Mexico. The first study focused on a 16 ha catchment on the resurgent Redondo Dome in the center of Valles Caldera, NM. The catchment has a frigid soil temperature and ustic soil moisture regime with bimodal precipitation of winter snowfall and convective summer rainfall. The dome includes a complex assemblage of pre-eruptive caldera materials and extant sedimentary rocks embedded within a welded, hydrothermally altered rhyolitic tuff. We sampled transects of soil profiles spanning summit, backslope, footslope, and toeslope positions. The data indicated strong landscape position control on soil drainage, downslope thickening of dark, organic matter rich surface horizons, and clear within profile lithologic discontinuities, and a significant contribution of dust to surface mineralogy and geochemistry. The second study examined aspect controls on pedogenesis across a chronosequence of basaltic cinder cones in near Flagstaff, AZ. The cones range in age from ~1 to ~1500 kyr, with a bimodal ustic soil moisture regime and thermic to mesic soil temperature regimes. Both and north and south aspects exhibited an increase in solum depth, increased clay and Fe-oxide content with age, and a threshold in argillic horizon formation near 200 kyr, with argillic horizons developing earlier on south facing slopes. The data also indicate a prominent role for Quatenary climate change and dust accumulation on early stages of pedogenesis and argillic horizon formation. These studies demonstrate the important interactive control of dust and topography on pedogenesis in semiarid volcanic environments.